With the increase of exploration and development of oil and gas resources and great improvement on the oil and gas exploration and development technology and equipment capability, the field of oil and gas development gradually shifts from land to ocean, from shallow sea water to deep sea water, from a normal-temperature and normal-pressure formation to a high-temperature and high-pressure formation or to even an ultra-high temperature and ultra-high pressure formation, and the operation of oil and gas exploration and development is also becoming more and more difficult.
In the drilling and completion operation of the high-temperature and high-pressure formation or even the ultra-high temperature and ultra-high pressure formation, because a pore pressure of a target interval formation is high and the pore pressure is close to a fracture pressure, during drilling and completion operation a safe drilling fluid density window is narrow or even there is no safe window, as a result, in order to balance the pore pressure of the formation during operation, mud with a high specific gravity has to be used, and when fluid column pressure of the mud with a high specific gravity within a well is higher than or approaches a formation leakage pressure, the mud in the well enters into the interior of the formation along the formation fracture under the action of pressure difference, higher liquid column pressure will also cause a primary fracture of the formation to open and a new fracture is formed. However, when the mud in the well stops circulating or the pressure of the fluid column in the well decreases due to other reasons, the primary fracture and newly formed fractures of the formation will close, and the high specific gravity mud filtrate that previously entered the interior of the formation due to the action of pressure difference may return to the interior of the borehole.
The phenomenon that mud enters the formation and then returns to the interior of the borehole under the action of pressure difference is a formation respiration effect. When the respiration effect occurs in the drilling process especially in the high-temperature and high-pressure formation, it is very difficult to accurately recognize the actual situation of downhole due to the complexity of the downhole situation, the process “inhalation” of the respiration effect is often mistaken as leakage of the mud, and thus the mud density is erroneously reduced to induce underground overflow; and the “exhalation” process of the respiration effect is mistaken as that there is an overflow underground, thus a well killing job is performed wrongly, which causes the formation fracture to be opened further, and a large amount of mud enters into the interior of the formation, resulting in a large amount of human, material and financial loss.